Gates and Buffett launched "The Giving Pledge" in June to convince hundreds of U.S. billionaires to give away most of their fortune during their lifetime or after their death and to publicly state their intention with a letter of explanation.

The full list of billionaires and their letters can be seen at www.thegivingpledge.org.

The Giving Pledge does not accept any money; it simply asks billionaires to make a moral commitment to give away their wealth to charity.

The billionaires announcing their pledge on Wednesday join real estate and construction billionaire Eli Broad, venture capitalist John Doerr, media entrepreneur Gerry Lenfest and former Cisco Systems Chairman John Morgridge who have already committed to giving away most of their wealth.

Buffett, who made his fortune with insurance and investment company Berkshire Hathaway Inc, Gates and his wife, Melinda, held several dinners with a couple of dozen rich Americans in the past year to urge them to make the pledge.

Buffett pledged in 2006 to give away 99 percent of his wealth to the Bill & Melinda Gates Foundation and family charities. Bill and Melinda Gates have so far given more than $28 billion of their fortune to their foundation.

Since the foundation began in 1994, it has given away more than $22 billion for health improvements in poor countries and to improve access for Americans to opportunities they need to succeed in school and life.

Gates was ranked the second-richest man in the world by Forbes magazine this year with $53 billion, while Buffett came in at No. 3 with $47 billion. Forbes said the United States is home to 403 billionaires, the most in the world.

More than 30 U.S. billionaires pledged on Wednesday to give away at least 50 percent of their wealth to charity as part of a campaign by investor Warren Buffett and Microsoft founder Bill Gates.
Among the billionaires joining the campaign are New York Mayor Michael...